1. Field of the Invention
This invention relates generally to testing and improving signal lines, and, more particularly, to applying tests and corrective measures to transmission lines.
2. Description of the Related Art
The testing and maintenance of signal lines, particularly transmission lines in telephone systems, is has become necessary and costly task. In telephony, it is common practice to transmit signals between a subscriber station and a central switching office via a two-wire bi-directional communication channel. The length of the transmission lines that carry telephone signals between the central switching office and the subscriber station can be quite large. As faster signals have been added to carry data over telephone lines, the quality of the transmission line has become critical, creating the need for periodic evaluation and adjustments.
Transmission lines generally have a natural characteristic impedance determined by cable construction and geometry. To drive a signal on a subscriber line while minimizing signal reflection from the far end of the subscriber line and maximizing the signal power entering the line, it is desirable to match the characteristic impedance of the transmission line with a termination at each end.
The Plain Old Telephone Service (POTS), which was designed primarily for voice communication, provides an inadequate data transmission rate for many modern applications. To meet the demand for high-speed communication, designers sought innovative and cost-effective solutions that took advantage of the existing network infrastructure. Several technological advancements were proposed in the telecommunications industry that made use of the existing network of telephone wires. One promising technology is the xDSL technology.
xDSL is making the existing network of telephone lines more robust and versatile. Once considered virtually unusable for broadband communications, an ordinary twisted pair equipped with DSL interfaces can transmit video, television, and high-speed data. The fact that more than six hundred million telephone lines exist around the world is a compelling reason that these lines will serve as the primary transmission conduits for at least several more decades. Because DSL utilizes telephone wiring already installed in virtually every home and business in the world, it has been embraced by many as a promising and viable option.
There are now at least four popular versions of DSL technology, namely Asymmetrical Digital Subscriber Line (ADSL), Integrated Services Digital Network Digital Subscriber Line (IDSL), Very High-Speed Digital Subscriber Line (VDSL), and Symmetric Digital Subscriber Line (SDSL). Although each technology is generally directed at different types of users, they all share certain characteristics. For example, all four DSL systems utilize the existing, ubiquitous telephone wiring infrastructure, deliver greater bandwidth, and operate by employing special digital signal processing. Because the aforementioned technologies are well known in the art, they will not be described in detail herein.
DSL technologies and POTS can co-exist in one transmission line (e.g., also referred to as xe2x80x9csubscriber linexe2x80x9d). Traditional analog voice band interfaces use the same frequency band, 0-4 Kilohertz (KHz), as telephone service, thereby preventing concurrent voice and data use. A DSL interface, on the other hand, operates at frequencies above the voice channels, from 100 KHz to 1.1 Megahertz (MHz). Thus, a single DSL line is capable of offering simultaneous channels for voice and data.
DSL systems use digital signal processing (DSP) to increase throughput and signal quality through common copper telephone wire. It provides a downstream data transfer rate from the DSL Point-of-Presence (POP) to the subscriber location at speeds of up to 1.5 Megabits per second (Mbps). The transfer rate of 1.5 Mbps, for instance, is fifty times faster than a conventional 28.8 kilobits per second (Kbps).
Other tests, such as line continuity tests and load isolation tests, are desirable for properly maintaining transmission lines. However, implementation of these tests can become manual-intensive and increase the costs of transmission line evaluation and maintenance. The industry lacks an efficient and automated method of employing line continuity and load isolation tests, particularly from a remote location. Furthermore, certain interfaces used for telephone transmission applications may cause line inversion problems. To solve line inversion problems, the point of the problem must be isolated and manually corrected, thereby adding to the costs of transmission line maintenance.
Another use of the telephone system is the application of high frequency signals, approximately 7.5 MHz, being placed on the transmission lines to facilitate local network connectivity for multiple electronic products within a subscriber station. When employing high-frequency network applications on the transmission lines, an evaluation of the wiring within a subscriber line is desirable. Currently, the industry lacks an efficient method of checking the integrity of the transmission line for the purpose of local networking.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
In one aspect of the present invention, an apparatus is provided for testing and evaluating a transmission line. The apparatus provided by the present invention comprises a network interface device capable of implementing one or more tests on said transmission line.
In another aspect of the present invention, a method is provided for testing and evaluating a transmission line. A set of command and data signals is received through an input/output interface. The command and data signals from the input/output interface are processed for controlling at least one relay. At least one switch is activated for testing a transmission signal line using the relay. The transmission signal line is tested based upon the activated switch.